Suction pump units are sufficiently known in prior art. They are used for extracting breast milk, but also in the medical field for extracting body liquids or fluids. Examples for the latter include extraction processes during and after surgical procedures, wound drainage, thorax drainage, and the suctioning of body fat.
While pumping breast milk, a vacuum pump is used to create a vacuum in a breast shield applied to the mother's breast, which causes the breast milk to be extracted from the breast. In order to enable as painless a suction as possible that corresponds to the sucking rhythm of the infant, a chronologically changing vacuum is applied to the breast shield. Suction curves that comprise a rapid rise in the vacuum to atmospheric pressure or to some other base value have proven especially effective in practice. FIG. 12 shows a corresponding pressure progression.
It was shown that a rise in pressure in an excess pressure range can be advantageous, as may be gleaned from FIG. 13. For example, one advantage is that any milk that gets into the vacuum tube between the breast shield and the breast pump can be purged. Another advantage is that a relatively thin vacuum tube can be used between the breast shield and the pump aggregate given active ventilation owing to an excess pressure source. Without active ventilation, the flow resistance in the thin tube would be too big, so that it would be impossible to dissipate the vacuum fast enough. Thin tubes yield a small dead volume. This in turn makes it possible to use smaller pump aggregates, i.e., vacuum pumps with a lower suction power.
A pressure progression with a positive ratio can be achieved by using the exhaust of the vacuum pump as a pressure source. However, in order to ensure the functionality of the vacuum pump, one of the pump connections, i.e., the vacuum port or the exhaust, must always be open. This can be accomplished with a 5/2 way valve. But the disadvantage to these valves is that they are relatively large, heavy and expensive. In addition, a steep flank is also preferred for this pressure progression during the rise in pressure. However, such a steep flank is virtually impossible to achieve with 5/2 way valves.
DE 102 28 455 discloses a milk extraction device with a vacuum pump, whose vacuum port and exhaust are connected with a switching valve. A suction line runs from the switching valve to a breast shield. Because the switching valve is connected with the exhaust acting as the excess pressure source, the vacuum in the breast shield can be changed relatively quickly. In this case, the switching valve comprises a rotating disk, which alternately releases a vacuum opening or an excess pressure opening.
US 2010/0121265 describes a breast pump for extracting breast milk with solenoid valves.
The pressure changes achievable by means of known suction pump units with the assistance of an excess pressure source take place relatively slowly. However, rapid changes in pressure are required to enable as natural an extraction as possible. A demand for suction curves with rapidly changing pressure ratios also exists in the other areas of application mentioned above for medical suction pump units.